1. Field of the Invention
The present invention relates to a lightning-resistant fastener, which is used for an airframe of an aircraft, especially for a wind thereof, and a method of mounting a lightning-resistant fastener.
2. Description of the Related Art
A wing constituting an airframe of an aircraft is of a hollow construction, and a wing surface panel forming a wing surface is fixed to a structural member existing in the wing by a fastener member (fastener).
The fastener member fastens the wing to the structural member by inserting a pin-shaped fastener main body into through holes, which have been formed in both the wing and the member attached to the wing, from the outside of wing, and by fixing the front end portion of the fastener main body by using a fixture from the interior side of the wing.
The aircraft must make thoroughgoing provisions against lightning strikes. In the case where the wing surface panel and the fastener member are made of different materials, at the time of lightning strikes, an arc discharge (spark) is produced in the direction extending along the interface between the wing surface panel and the fastener member by an electric potential difference between the wing surface panel and the fastener member. Since a fuel tank is housed in the internal space of the wing, it is necessary to reliably suppress the production of arc discharge at the time of lightning strikes.
To meet such necessity, a structure has conventionally been proposed in which, as shown in FIG. 9, on the inside of a wing 1, a cap 6 is installed in a state of being separate from a fastener main body 4a of a fastener member 4, which penetrates a first member 2 corresponding to the wing surface panel and a second member 3 installed within the wing, and a fixture 4b, and an air-gap 7 filled with air is formed between the cap 6 and the fastener main body 4a, the fixture 4b (for example, refer to Japanese Patent Laid-Open No. 2-7398).
However, the technique descried in Japanese Patent Laid-Open No. 2-7398 does not provide a structure in which the cap 6 can be positioned with respect to the fastener member 4, and the installation position of the cap 6 depends on the worker. Therefore, the center of the cap 6 and the center of the fastener member 4 may shift greatly. If in the air-gap 7, a place where a gap between the fastener member 4 and the cap 6 is narrow is produced, the function (insulation properties) of the cap 6 decreases. In the worst case, if the cap 6 is installed in a state of being in contact with the fastener member 4, the function itself of the cap 6 may be impaired greatly.
The cap 6 is installed on the second member 3 with an adhesive 9 as shown in FIG. 9A, or is outer-peripherally covered with a rubber (insulating material) 10 as shown in FIG. 9B. Therefore, in the installation site, the bonding work or the coating work of the rubber 10 is required, so that the work takes much time and labor. Needless to say, the interior of the wing 1 of aircraft has a narrow space, and the above-described work performed at a secluded position provides very poor workability. Moreover, since the fastener member 4 is provided at several thousands to several ten thousands places throughout the wing 1, the deterioration in workability leads directly to the rise in cost.
Furthermore, the above-described work is what is called manual work, so that the work quality is easily varied depending on the worker, which also exerts an influence on the reliability.
To solve the problems, the inventors have already proposed a technique in which a fastener member has an engaging part formed in a portion projecting to the interior side of an airframe, a cap has an engaged part to be engaged with the engaging part of the fastener member in a central portion of the inner peripheral surface thereof, and the engaging part of the fastener member is engaged with the engaged part (see Japanese Patent Laid-Open No. 2010-254287).
However, according to the techniques described above, the axis of the fastener member is not always perpendicular to the inner peripheral surface of the wing 1. For example, the second member 3 mounted on the inner peripheral surface of the wing 1 may be inclined with respect to the axis of the fastener member 4 as shown in FIG. 9. In such a case, when the cap 6 is engaged with the fastener member 4, a gap occurs between an outer circumferential edge 6a of the cap 6 and the second member 3, and therefore, a sufficient lightning-resistant performance cannot be assured.
In addition, if the ambient temperature repeatedly varies significantly, the cap 6 may be loosened, and a gap may occur between the outer circumferential edge 6a of the cap 6 and the second member 3.
The present invention has been accomplished in view of the technical problems described above, and an object of the present invention is to provide a lightning-resistant fastener capable of assuring a sufficient lightning-resistant performance.